To the surfaces of various articles used indoors or outdoors, various kinds of dirt such as dust, soot, and cigarette tar, adhere. Therefore, various methods have been investigated for suppressing the adhesion of such dirt. For example, it is known that electrostatic adhesion of hydrophilic dirt such as dust can be suppressed by coating the surfaces of various articles with an antistatic agent. It is also known that lipophilic dirt such as soot can be readily removed by coating the surfaces of various articles with an oil-repellent fluororesin.
However, the above-mentioned methods of suppressing the adhesion of the above-mentioned various kinds of dirt pose a problem in that the antisoiling performance cannot be maintained over a long period of time due to peeling and deterioration of the coating film.
Consequently, a method has been attempted which maintains the antisoiling performance over a long period of time by forming a film in which hydrophilic portions and hydrophobic portions are mutually independently exposed in a minute region. For example, there has been disclosed a method of forming a film having hydrophilic portions and hydrophobic portions in a water-contacting region by a vapor phase method using a predetermined pattern filter (e.g., see Patent Document 1). There has also been disclosed a method of forming a resin coating film having a microphase-separated structure containing hydrophilic portions and hydrophobic portions by applying, to the surface of an article, a coating composition containing a polymer having a functional group, hydrophilic particles, metal alkoxide and a solvent (e.g., see Patent Document 2).
On the other hand, in a heat exchanger of an air conditioner for use in buildings, automobiles, etc., drops of water, which form from condensed water generated in cooling, form a bridge between fins attached to passages (pipes) through which a refrigerant passes, which narrows the ventilation flue of air, resulting in deterioration in the heat exchanging efficiency of the heat exchanger. Further, the drops of water produce a phenomenon of drops of water jumping out from an air conditioner, i.e., condensation splash. Then, the formation of the bridges due to drops of water has been prevented by boehmite treatment and hydrophilization treatment to the fin surfaces using water glass, a hydrophilic polymer, or a composition containing a hydrophilic polymer and an inorganic compound.
In the heat exchanger of an air conditioner, the adhesion of various kinds of dirt such as dust, soot, and cigarette tar causes not only a problem that the appearance is degraded but also hygienic problems originating from the dirt such as propagation of mold and bacteria, and from reductions in heat exchanger performance. In particular, such dirt becomes a factor in reducing the hydrophilicity of fin surfaces, which have been subjected to hydrophilization treatment, and producing drops of water on the surface of the fin, the factor which leads to deterioration in the heat exchanging efficiency of a heat exchanger and condensation splash.
Therefore, in order to avoid the hygienic problem and deterioration in the performance of a heat exchanger, mere hydrophilization of the heat exchanger is not sufficient and the adhesion of various kinds of dirt must be suppressed.
As a method of suppressing the adhesion of dirt to the heat exchanger of an air conditioner, there has been disclosed a method of forming a film in which an inorganic oxide and a hydrophobic resin are microscopically dispersed and exposed on the top surface of a fin by applying, to the surface of the fin, a coating composition containing an inorganic oxide including a photocatalytic oxide and a hydrophobic resin (e.g., see Patent Document 3). There has also been disclosed a method of forming a film in which silicone and a water-repellent fluororesin are microscopically dispersed and exposed on the top surface of a fin by applying, to the surface of a fin, a coating composition containing photocatalytic oxide particles, silicone and a water-repellent fluororesin (e.g., see Patent Document 4).
[Patent Document 1] JP 09-56625 A
[Patent Document 2] JP 2003-160681 A
[Patent Document 3] JP 2001-88247 A
[Patent Document 4] JP 10-132483 A